Triangulated bicycle pedal support structure

ABSTRACT

A bicycle with a triangulated crank structure replaces the single span crank arm which connects the spindle to the foot pedal on bicycles today. The triangulated crank structure is typically comprised of several sections including two linear spans of structural material arranged so that one end of each linear span connects with the other to form the vertex of an acute angle, proximate to a pedal attachment area. From the vertex, the linear spans diverge and each connects at its opposite end to separate locations on a structural element attached to an end of the bicycle&#39;s crankshaft or spindle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates primarily to bicycles, but also to any other humanpowered vehicles, watercraft, or exercise devices which utilize a footpedal or handgrip for the operator to convert rotational motion and/orlinear motion of his feet or hands, into work, in order to activate thedevice.

2. Description of Prior Art

Bicycle crank arms in general, provide a means for physically connectingthe foot pedals of the bicycle to the crankshaft of the bicycle. In somecases, one of the crank arms is also attached to a chain sprocket, or aset of axially concentric sprockets, which drives a chain for thepurpose of transmitting power to the drive wheel of the bicycle. Whetherthe sprocket is attached directly to the crankshaft or spindle, orindirectly to the spindle through one of the crank arm assemblies, thecrank arms enable force exerted on the foot pedals to be transferredinto power to propel the bicycle as the foot pedals sweep through eachstroke.

Bicycles have evolved from their earliest designs with a pair ofbilaterally symmetric and inversely synchronized foot pedals, eachconnected to the crankshaft or spindle of the vehicle by a generallystraight crank arm. As bicycle consumers have come to put more emphasison light weight and performance, bicycle manufacturers have endeavoredto manufacture lighter and better performing bicycles. This quest hasled many manufacturers to utilize computer aided design techniques andexotic materials in the creation of their products. Today, the weightsof many components on bicycles are usually communicated in gram units,because the emphasis on weight reduction is so great that the units ofpounds and ounces are insufficiently explicit for many consumers.

One of the largest concentrations of structural material in a typicalbicycle is in the crank arm. That often corresponds to one of thelargest concentrations of weight on a bicycle, despite somemanufacturers' use of exotic lightweight materials at this location.Reducing weight by using such materials usually leads to a significantcost penalties or other tradeoffs.

SUMMARY OF THE INVENTION

This invention replaces the double ended crank arm design currently usedon bicycles, with a triangulated crank structure. Triangulation isaccomplished by replacing a straight bar type structure that connectsthe spindle to the pedal shaft end of a crank arm, with a splitstructure that has two separate tube segments, spaced away from a linebetween the spindle end and the corresponding pedal shaft attachmentlocation, that line being the neutral axis of the structure. During therider's power stroke, one such tube segment would be mostly undertension while the other would be mostly under compression. This largelyeliminates high bending stresses associated with the straight crankdesign. It does so by moving structural material much further away fromthe neutral axis of the crank than is possible with a straight crankdesign.

Mechanical triangulation when applied to bicycle cranks permits amaximum structural efficiency defined as the minimum amount ofstructural material possible to support a given load. The inherentstructural efficiency problem in a triangulated design is therequirement for multiple structural segments. Furthermore, the shortestdistance between the spindle end and the pedal shaft attachment means,and therefore the shortest total length of structural material requiredto connect them, is the straight segment of the prior art.

This invention preferably uses hollow tubes to save weight in themultiple segments. The hollow tubes are structurally optimized to resistboth torsion loads due to the offset pedal, and the lateral bendingloads perpendicular to the applied force that the tubes experienceduring cyclical power transmission peaks. The hollow tubes also approachan ideal design for resisting crank deflection when the rider's weightis pushing on the pedal while at or near the top or bottom of thestroke. Also, this invention preferably uses only two structuralsegments or struts to connect the hollow tubes to the spindle and/orsprocket assembly. Lastly, the crank structure on the same side of thevehicle as the drive sprocket uses two structural segments or struts toconnect the structure efficiently to four sprocket bolts on a five boltsprocket, or to two sprocket bolts on a four bolt sprocket.

The primary object of the invention is to improve structural efficiencyof bicycle cranks, thereby decreasing weight without any reduction instrength or stiffness. The invention can provide bicycle cranks withboth strength enhancement and weight reduction benefits.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a side perspective view of one preferred embodiment of thetriangulated bicycle crank structure disclosed in this invention.

FIG. 2 is a cross sectional perspective view of an elliptical main tubeassembly according to one preferred embodiment of this invention.

FIG. 3 is a side view of a triangulated bicycle crank structure wherethe orientation of the two tubes is adjusted to attach to a second pairof tubes that extend further from the spindle attachment locationaccording to another preferred embodiment of this invention.

FIG. 4 is a side view of a triangulated crank structure according toanother preferred embodiment of this invention wherein two of theadjoining tube segments shown in FIG. 3 are approximately collinear andcomprise a single tube.

FIG. 5 shows a side view of the triangulated crank structure shown inFIG. 1 which also includes four flanges for attaching a sprocket(assembly) directly to the triangulated crank structure.

FIG. 6 shows a side view of the triangulated crank structure shown inFIG. 1 which also includes tapped holes for attaching a sprocket(assembly) to the triangulated crank structure.

FIG. 7 shows a side view of a triangulated crank structure thatincorporates non-parallel adjacent structural segments for connectingthe hub area of the crank structure to the attachment location of themain tubes of the structure.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 discloses a structure 1 for rotatively connecting the pedal of abicycle to the spindle of a bicycle. Structure 1 comprises a hub 6 whichincludes an opening 5 to receive the end of a spindle, which rotates onan axis 2. Hub 6 further includes internal threading 8 recessed from itsouter face for the purpose of securing a threaded cap which can coverthe outer opening of the hub. According to one preferred embodiment ofthis invention structure 1 comprises two struts, preferably a firstconnection strut 10 and a second connection strut 16, attached to hub 6,which extend radially away from the center of hub 6, preferably at anattachment angle 84 of less than 200° and optimally less than 180°.While these struts 10, 16 are generally round and hollow in thepreferred embodiment, they may be of any cross sectional profile,including rectangular, round, elliptical, “C” or “D” or “I beam” shaped,etc. First connection strut 10 and second connection strut 16 may or maynot taper, and may or may not be partially or completely hollow. Outsideexterior reinforcing webs 11 and inside exterior reinforcing web 12 areincluded in one preferred embodiment of this invention to reducematerial stresses where first connection strut 10 and second connectionstrut 16 attach to hub 6 at spindle shaft end 50. While thesereinforcing webs 11 and 12 are shown in FIG. 1 in a plane thatapproximately bisects the first and second connection struts 10 and 16,the quantity, size, configuration, and location of the reinforcing websare not necessarily constrained as shown by FIG. 1. It is actuallyintended for the reinforcing webs 11 and 12 to have differentcharacteristics depending on whether they are on the crank structureassociated with the right side or the left side of the bicycle. On theright side of the bicycle, typically the sprocket side, webs 11 and 12would be positioned relatively flush with the inside face of hub 6 tofacilitate sprocket attachment.

FIG. 1 also shows two knuckles 15 for attaching first arm 20 and secondarm 21 to the outer end of first and second connection struts 10 and 16.Depending on the cross sectional profile of connection struts 10 and 16,it may be practical to manufacture knuckles 15 as extensions of firstand second connection struts 10 and 16, rather than as separate piecesto be attached during assembly. Unless first arm 20 and second arm 21have a round cross sectional outer profile at their respective ends,they cannot be threaded and screwed into knuckles 15. Since the crosssectional shape of first arm 20 and second arm 21 in the preferredembodiment is elliptical, a preferable means of attaching first arm 20and second arm 21 to the corresponding knuckle 15 at a first crank end52 and a second crank end 54, respectively, is a powerful adhesiveapplied to the outside walls of the ends of first arm 20 and second arm21 prior to insertion into an appropriately shaped hole in knuckle 15.Knuckles 15 can be similarly attached to struts 10 and 16 in the eventthat first and second connection struts 10 and 16, and knuckles 15 donot comprise a single piece.

FIG. 1 further discloses a junction 30 at a pedal attachment area 59.Junction 30 is the physical means for connecting first arm 20 and secondarm 21 at their first distal end 56 and second distal end 58,respectively. Junction 30 thereby creates a connection angle 82 betweenfirst arm 20 and second arm 21. Junction 30 preferably includes internalthreads 31 or a similar pedal attachment area 59 for receiving the shaftof a pedal assembly, with said shaft preferably aligned with axis 3.According to one preferred embodiment of this invention, the junction 30attaches to first arm 20 and second arm 21 in a similar manner as firstarm 20 and second arm 21 connect to knuckles 15. Because first arm 20and second arm 21 are non-parallel when assembled into structure 1, twoof them cannot be inserted into knuckles 15 and junction 30 withoutseverely bending at least one of them. Although this assembly problemcan be solved by splitting one knuckle 15 or junction 30 into twopieces; using oversize holes with shims; or by putting a backside holein one of them, such solutions are not shown in FIG. 1. Nor are notches,screws, dowels, or other means for positively and redundantly connectingfirst arm 20 and second arm 21 to knuckles 15, or to junction 30 shownin FIG. 1. It should be noted that the components of FIG. 1 could bemanufactured as a single piece, if a material with flexible fabricationproperties such as carbon fiber is used.

FIG. 2 shows a perspective end view of second arm 21. The preferredembodiment comprises a hollow or tubular second arm 21, and first arm 20preferably identical to second arm 21, having generally elliptical crosssections. This cross sectional shape is optimized for resisting acombination of torsional loads and bending loads in the plane of themajor axis of the ellipse. The resistance to bending loads in the planeof the major axis of the ellipse is further enhanced by increases in thewall thickness where the major transverse axis of the ellipse comprisingthe cross section of second arm 21 intersects the second arm 21. Thesecond arm 21 of FIG. 2 does not show any deviation from an ellipticalcross section, although replacing the smooth elliptical outer and/orinner profile of one or both narrow sides of the ellipse with a morerectangular design, thus adding structural material, would furtherimprove resistance to bending forces in the plane of the majortransverse axis. Any tube cross sectional shape that overlapped theapproximate shape of an ellipse will benefit from the structuralcharacteristics of the ellipse in this application. Similarly, first arm20 and/or second arm 21 could be used in combination with other shapessuch as “I” beams to adjust properties in different bending modes.Alternative tube designs, including those with more circular crosssections could be substituted for the elliptical design, which mayadditionally include an internal and/or external bead or web along adiameter to better resist bending in the plane of that diameter. Thepreferred embodiment comprises a first arm 20 and a second arm 21 thatare straight along their length. Depending on requirements for clearancewith other components of the vehicle, first arm 20 and/or second arm 21could curve, bend or vary in cross sectional profile at variouslocations along their lengths. Another preferred embodiment replacesfirst arm 20 and/or second arm 21 with adjacent round tubes, thusallowing threaded connections with knuckles 15 and/or junction 30.Another preferred embodiment replaces the hollow tubes of first arm 20and/or second arm 21 with “C” sections, and additionally preferablyincludes a facia covering the opening between first arm 20 and secondarm 21.

Because it is difficult to use high strength alloys such as aluminumalloys to manufacture a seamless tube, such as the preferred embodimentof second arm 21, with the aspect ratio and elliptical cross sectionalshape and the different wall thickness necessary to structurallyoptimize its design, a multi-piece assembly is utilized in one preferredembodiment of this invention to manufacture an elliptical tube. Twohalves of an elliptical tube including a lower piece 23 and an upperpiece 24 are mated together to produce a tube with an elliptical crosssection. In order to properly align pieces 23 and 24 relative to oneanother, and to mate them more securely to each other, one or morerectangular keys 22 may be included on each side of the assembly. Thekeys 22 fit into corresponding slots on pieces 23 and 24. The preferredmethod for attaching pieces 23, 24 and keys 22 is with a powerfuladhesive, although more traditional attachment means such as welding,screws, collars, etc., are possible. When an adhesive is used, keys 22afford shear planes, typically perpendicular to the primary mating planeof pieces 23 and 24, that improves the performance of the adhesive.While it is possible to machine one or more keys or shear planes intothe mating surface of lower piece 23 and/or upper piece 24, one or moreseparate keys 22 on each side of first arm 20 and/or second arm 21 arenormally simpler from a manufacturing standpoint.

Because of the triangulated orientation of first arm 20 and second arm21 in the crank structure 1, the design of first arm 20 and/or secondarm 21 is optimized for resisting deflection regardless of whether thecrank structure 1 is in the vertical or horizontal position while beingsubjected to a vertical load.

FIG. 3 shows a side elevational view of a crank structure 1 with aspindle attachment hole 5, and a pedal shaft receiving hole 31, orsimilar pedal attachment area 59 at its other end. In this figure, firstand second connection struts 10 and 16 are longer than a preferredembodiment shown in FIG. 1, and incorporate a smaller attachment angle84 between them. First and second connection struts 10 and 16 haveapproximately the same proportions as first arm 20 and second arm 21,which are correspondingly shorter than the design of FIG. 1. A bridge 26serves both as a means to attach the middle ends of first and secondconnection struts 10 and 16, and first arm 20 and second arm 21together, and to complete the triangle otherwise formed by first andsecond connection struts 10 and 16, and first arm 20 and second arm 21on either of its sides, thereby maximizing the rigidity of thestructure. Additional bridges 26, not shown, can be included at otherlocations than the junction of first and second connection struts 10 and16, and first and second arms 20 and 21, in order to further stiffen thestructure. Bridge 26 is shown in this figure as a flat plate viewed fromthe side, although it could be a truss section, thereby effectivelyshortening first connection strut 10 and/or second connection strut 16,and first arm 20 and/or second arm 21, at the expense of cost andcomplexity. It is presumed that there would be weight saving techniques,such as the inclusion of holes in bridge 26, utilized during themanufacture of crank structure 1. In this design, first and secondconnection struts 10 and 16, and first arm 20 and second arm 21 may beidentical. This structure offers the same advantage as the design ofFIG. 1 in terms of reduced material weight by virtue of the structuralmaterial being located away from the neutral axis of the crank structure1. The neutral axis for the entire crank structure 1 is the axis throughthe structure which intersects the axis of rotation of the spindle andthe axis of rotation of the pedal. Although this design has the samehigh material stress levels as a traditional single span crank wherefirst connection strut 10 intersects hub 6, it is structurally superior,and therefore potentially lighter and stronger, to a traditional singlespan crank along most of its length.

FIG. 4 shows a side elevational view of a triangulated crank structure 1wherein second connection strut 16 of the previous designs extendsdirectly from the vicinity of hub 6 to the vicinity of junction 30thereby eliminating the need for a separate second arm 21. A bridge 26is included in this design to provide the necessary triangulation andinterconnection means to first connection strut 10 and first arm 20. Itis possible to modify current single span cranks to become triangulateddesigns by attaching a first connection strut 10, a first arm 20, and abridge 26 to current non-triangulated crank designs to increase theirstiffness and/or reduce their weight. While the design of FIG. 4 showsthe triangulating first connection strut 10, first arm 20, and bridge 26above the second connection strut 16, there is no reason that the designcould not be inverted with respect to a horizontal axis.

FIG. 5 shows a side elevational view of a crank structure 1 whichincludes a plurality of locations to fasten the structure 1 to asprocket or sprocket assembly. FIG. 5 further shows a radially symmetricarrangement of five dashed lines 41 intersecting at the center of hub 6,and a circular dashed line 42 concentric with hub 6. The locations ofthe intersections of lines 41 and a circle 42, of which only one isshown, represent the bolt hole 37 locations of a typical five boltpattern for attaching a sprocket assembly to the crank structure 1.Flanges 35 allow the sprocket to be attached directly to first andsecond connection struts 10 and 16, thus avoiding a sprocket attachmentmeans emanating from hub 6, such as flange 36. This eliminatesopportunities for creaking or breaking at the junction between the hub 6and any radially concentric sprocket mounting hole array attachedthereto. Furthermore, attaching flanges 35 directly to first and secondconnection struts 10 and 16 improves structural efficiency over otherdesigns since first and second connection struts 10 and 16 are alreadyin the immediate vicinity of the sprocket attachment points, representedby the location of bolt holes 37, and therefore less material isnecessary than would otherwise be required to connect flanges 35 to hub6. Braces 38 may be included to provide additional reinforcement toflange 36. The arrangement of flanges 35 in FIG. 5 represent just one ofnumerous possible configurations that take advantage of the proximity offirst and second connection struts 10 and 16 to industry standardsprocket mounting holes locations 37. It should be noted that whileflanges 35 are attached to first and second connection struts 10 and 16in the preferred embodiment, they could be attached to other componentsof the crank structure 1 on other crank structure designs that aremodifications of the preferred embodiment, wherein said other componentsmay be in close proximity to standard or non-standard sprocket mountinglocations.

FIG. 6 also shows a side elevational view of a crank structure 1 whichincludes a plurality of locations to fasten the structure 1 to asprocket or sprocket assembly. FIG. 6 further shows a radially symmetricpattern of four dashed lines 41 intersecting at the center of hub 6, anda circular dashed line 42 which is concentric with hub 6. Only one suchcircular dashed line 42 is shown, although additional ones concentricwith hub 6 are representative of bolt pattern diameters typical ofmulti-speed bicycles today. The locations of the intersections of lines41 and circle 42 represent the bolt hole 37 locations of a typical fourbolt pattern for attaching a sprocket assembly to the crank structure 1.Connection strut holes 39 allow the sprocket to be attached directly tofirst and second connection struts 10 and 16, thus avoiding a sprocketattachment means emanating from hub 6, such as flange 36. Thearrangement of strut holes 39 in FIG. 6 represent just one of numerouspossible configurations that take advantage of the proximity of firstand second connection struts 10 and 16 to industry standard sprocketmounting holes locations 37.

FIG. 7 shows a side elevational view of a crank structure 1 with a hub6, a first arm 20 and second arm 21, and a junction 30 which are allinterconnected. The interconnection means between hub 6 and knuckles 15of the previous structure is comprised of first and second connectionstruts 10 and 16 each comprised of a single element. In this figure,single element design of first and second connection struts 10 and 16 isreplaced with a multi-element connection strut design consisting offirst connection strut segments 10 a and 10 b, and second connectionstrut segments 16 a and 16 b. While it is certainly possible to havemore than two such strut segments coming off one side of hub 6, thebenefit of additional struts is marginal at best compared to a singlestrut or double strut design. In this embodiment, first connection strutsegments 10 a and 10 b, and second connection strut segments 16 a and 16b, are non-parallel, thus providing a degree of triangulation in theattachment of knuckles 15. Each knuckle 15 of this embodiment has athird hole to accommodate the additional strut segment of the design. Inanother preferred embodiment, knuckles 15 are integral with firstconnection strut segments 10 a and 10 b, and second connection strutsegments 16 a and 16 b. In this preferred embodiment, hub 6 also hasholes or solid connection means to rigidly secure one of each of theends of first and second pairs of connection strut segments 10 a and 10b, and 16 a and 16 b. This design offers the manufacturing advantage ofeconomically fabricating hub 6 and/or knuckles 15 as castings, thenutilizing round tubes or tubes comprising a cross section such as thatof first arm 20, or alternative non-tubular interconnection means, tointerconnect hub 6 and knuckles 15 with minimal weight. When non-tubularconnection strut segments 10 a and 10 b, and 16 a and 16 b are utilizedin the design, the manufacturing option to fabricate hub 6, knuckles 15,and interconnecting strut segments 10 a, 10 b, 16 a, and 16 b from asingle piece of structural material such as metal becomes morepractical. Knuckles 15 or first and second arms 20 and 21, can befabricated to include flanges with bolt holes or other means forattachment directly to a sprocket or sprocket assembly, since that canbe more practical than attaching a sprocket or sprocket assemblydirectly to first connection strut segments 10 a and 10 b, secondconnection strut segments 16 a and 16 b, or to a rigid fixture attachedthereto, depending on the proximity of said components relative to thesprocket attachment points.

While in the foregoing specification this invention has been describedin relation to certain preferred embodiments thereof, and many detailshave been set forth for purpose of illustration, it will be apparent tothose skilled in the art that the apparatus according to this inventionis susceptible to additional embodiments and that certain of the detailsdescribed herein can be varied considerably without departing from thebasic principles of the invention.

1. A bicycle crank structure projecting from a spindle shaft endcomprising: a first arm having a hollow cross-section, the first armhaving a first crank end connected with respect to the spindle shaft endand a first distal end terminating at a pedal attachment area; and asecond arm having hollow cross-section, the second arm having a secondcrank end connected with respect to the spindle shaft end and a seconddistal end terminating at the pedal attachment area, the second distalend connected with respect to the first distal end to form an anglebetween the second arm and the first arm.
 2. The bicycle crank structureof claim 1 further comprising: a first connection strut connecting thefirst arm to the spindle shaft end; and a second connection strutconnecting the second arm to the spindle shaft end.
 3. The bicycle crankstructure of claim 2 wherein the first connection strut and the secondconnection strut are radially asymmetric with respect to the spindleshaft end.
 4. The bicycle crank structure of claim 1 wherein at leastone of the first arm and the second arm comprise a generally ellipticalcross-section.
 5. The bicycle crank structure of claim 4 wherein atleast one of the first arm and the second arm comprise a multi-pieceassembly.
 6. The bicycle crank structure of claim 5 wherein themulti-piece assembly is bonded together to form at least one of thefirst arm and the second arm.
 7. The bicycle crank structure of claim 1wherein the second arm is connected with respect to the spindle shaftend on an opposing side of the spindle shaft end as the first crank end.8. A bicycle crank structure projecting from a spindle shaft endcomprising: a first arm having a generally hollow cross-section, thefirst arm connected at one end with respect to the spindle shaft end andat an opposite end with respect to a pedal attachment area; a second armhaving a generally hollow cross-section, the second arm connected at oneend with respect to the spindle shaft end and at an opposite end withrespect to the pedal attachment area; and the first arm positioned at aconnection angle with respect to the second arm.
 9. The bicycle crankstructure of claim 8 wherein the first arm comprises a generallyelliptical cross-section.
 10. The bicycle crank structure of claim 8wherein the second arm comprises a generally elliptical cross-section.11. The bicycle crank structure of claim 8 further comprising: a firstconnection strut connecting the first arm to the spindle shaft end; anda second connection strut connecting the second arm to the spindle shaftend.
 12. The bicycle crank structure of claim 11 wherein the firstconnection strut and the second connection strut are radially asymmetricwith respect to the spindle shaft end.
 13. The bicycle crank structureof claim 8 wherein at least one of the first arm and the second armcomprise a multi-piece assembly.
 14. The bicycle crank structure ofclaim 8 wherein the multi-piece assembly is glued together to form atleast one of the first arm and the second arm.
 15. A bicycle crankstructure projecting from a spindle shaft end comprising: a first armhaving a first crank end connected with respect to the spindle shaft endand a first distal end terminating at a pedal attachment area, the firstarm at least partially hollow and having a generally ellipticalcross-section; and a second arm having a hollow cross-section, thesecond arm having a second crank end connected with respect to thespindle shaft end and on an opposite side of an axis of rotation as thefirst crank end, the second arm having a second distal end terminatingat the pedal attachment area to form a connection angle with respect tothe first arm.
 16. The bicycle crank structure of claim 15 wherein thesecond arm comprises a generally elliptical cross-section.
 17. Thebicycle crank structure of claim 15 further comprising a multi-pieceassembly glued together to form at least one of the first arm and thesecond arm.
 18. A support system for a bicycle crank structureprojecting from a spindle shaft end comprising: a first strut connectedwith respect to the spindle shaft end; a second strut connected withrespect to the spindle shaft end, the second strut positioned at anattachment angle less than approximately 200° from the first strut; anda first crank arm having a hollow cross-section connected with respectto the first strut and a second crank arm having a hollow cross-sectionconnected with respect to the second strut, the first crank arm forminga connection angle at a pedal attachment area with respect to the secondcrank arm.